World champion lightweight rowers Anthony Edwards and Sam Beltz have put a down payment on Olympic selection by sensationally trumping Australia’s best heavyweights at the national titles in Perth.

Edwards and Beltz defied their smaller frames to blitz the heats of the men’s pair at Champion Lakes on Wednesday – smashing the world’s best time for the lightweight pairs class in the process.

The Tasmanian duo, half of the lightweight fours crew which triumphed at last year’s world championships, finished their heat in six minutes 22.14 seconds.

It was 4.07s quicker than the world mark, set by Irishmen Tony O’Connor and Neville Maxwell in 1994, but it won’t stand as an official record because it was achieved in an open weight event.

Edwards and Beltz, and lightweight crewmates Ben Cureton and Todd Skipworth, were racing against the heavyweights to best prepare for the final round of Olympic selection trials, starting on March 23 at Penrith.

The Tasmanians not only beat their rivals home in a tight heat but their time was also better than defending national champions Drew Ginn and Josh Dunkley Smith who won their heat in 6:22.66.

“It’s a nice feeling when you can make a boat go that fast,” Edwards, 38, told AAP.

“We’ve never had the opportunity to really wind it up like that. It was a close race so we had to push all the way and get as much as we could out of ourselves.

“We executed our race plan to perfection this morning and we both felt in the zone today.

“Hearing afterwards that we’d gone four seconds faster than world-record pace was very exciting.”

Such a performance will make it almost impossible for selectors to overlook Edwards and Beltz, 31, for the London Games where Australia will be aiming to win a first gold in the lightweight four.

Three-time Olympic champion Ginn believed the defending champions were 10 seconds slower than par but admitted they were rusty after a solid block of training in the men’s four – Australia’s priority boat for London.

World championship bronze medallists Sarah Tait and Kate Hornsey were the best of the women’s pair crews in an impressive heat win.

Kim Crow (Vic), Brooke Pratley (NSW) and Pippa Savage (Qld) won their women’s single scull while Queenslander Jared Bidwell recorded the quickest time in the heats of the men’s single scull as he upset South Australian James McRae.